Western and Arab nations ratcheted up pressure on Syria's Bashar al-Assad as the Red Cross said it had finally gained access to a besieged area of the city of Homs to begin evacuating casualties.

Western and Arab nations ratcheted up pressure on Syria's Bashar al-Assad as the Red Cross said it had finally gained access to a besieged area of the city of Homs to begin evacuating casualties Friday.

A meeting of more than 60 foreign ministers in Tunisia saw calls for Arab peacekeepers to intervene and for the opposition to be armed, as well as a US warning that Assad would pay a heavy price for defying international will.

In the first sign that growing pressure might be having an effect, Red Cross and Red Crescent ambulances entered the besieged Homs district of Baba Amr and evacuated seven Syrians wounded in bombardments by regime forces.

"Three ambulances entered Baba Amr and they have left. They evacuated so far seven wounded Syrian citizens," International Committee of the Red Cross spokesman Saleh Dabbakeh told AFP in Damascus.

But two wounded Western journalists had not yet been evacuated, nor had the bodies of two others, he said.

"Negotiations continue with the Syrian authorities and the opposition in an attempt to evacuate all persons, without exception, who are in need of urgent help," he added.

In Tunis, the first meeting of the Friends of Syria issued a declaration calling for an immediate end to violence and for new sanctions.

The group called for Syria's government to "immediately cease all violence" to allow humanitarian access and "committed to take steps to apply and enforce restrictions and sanctions on the regime".

US secretary of state Hillary Clinton said Assad would pay a "heavy cost" for ignoring the will of the international community.

"The Assad regime has ignored every warning, squandered every opportunity, and broken every agreement," she said.

"Faced with determined protesters demanding their rights and their dignity, the regime is creating an appalling humanitarian disaster."

Clinton also announced $10 million in aid for humanitarian efforts in Syria.

And in Washington President Barack Obama told reporters: "We're going to continue to keep the pressure up and look for every tool available to prevent the slaughter of innocents in Syria."

"It's important that we're not bystanders during these extraordinary events," he added.

In Syria itself, at least 53 more people were killed in renewed violence on Friday, two days before Syrians vote on a new constitution that could end 50 years of Baath party rule, while keeping wide powers with the president.

Host nation Tunisia called for an Arab peacekeeping force to be sent in to help end the killings, and for Assad to be granted immunity to persuade him to stand down.

"The current situation demands an Arab intervention in the framework of the League, an Arab force to keep peace and security, to accompany diplomatic efforts to convince Bashar to leave," Tunisian President Moncef Marzouki said.

"A political solution must be found, such as granting the Syrian president, his family and members of his regime judicial immunity and a place to seek refuge, which Russia could offer."

More than 7,600 people have been killed since the uprising against Assad's rule erupted last March, according to the Syrian Observatory for Human Rights.

The main opposition umbrella group the Syrian National Council has warned that military intervention might be the "only option" to end the crackdown.

Western and Arab nations however have so far rejected the idea of a foreign mission like the operation that helped topple Moamer Kadhafi's regime in Libya.

"I think it's an excellent idea... because they have to protect themselves," he said before a meeting with Clinton.

Three top US senators called for "responsible nations" to help the Syrian opposition, including providing weapons to enable them to defend themselves against the Assad regime.

Republican Senators John McCain and Lindsey Graham and Independent Joe Lieberman said in a statement that "tangible actions" were urgently needed to "ensure that the Syrian people have the means to protect themselves against their attackers".

Clinton on Thursday described the SNC as a "credible representative" that would demonstrate "there is an alternative" to Assad's regime.

French foreign minister Alain Juppe also endorsed the SNC on Friday, calling it "the pole around which the opposition must organise".

The final declaration recognised the SNC as "a legitimate representative of Syrians seeking peaceful democratic change" but fell short of giving it exclusive recognition and urged it to work to unite the opposition.

Russia and China were notable by their absence from Friday's meeting, highlighting the difficulty in building an international consensus on Syria.

Both countries have frustrated efforts to rein in Assad's regime, including by vetoing UN Security Council resolutions.

"We need to change the attitude of the Russians and Chinese," Clinton told journalists after the meeting.

"They must understand they are setting themselves against the aspirations not only of the Syrian people but of the entire Arab Spring."

A French doctor who returned to Paris Friday after a 19-day mission in Syria described to AFP the "carnage" he had seen in Homs with "children almost cut in two by shells."

Jacques Beres, a co-founder of Medecins sans Frontieres (Doctors Without Borders), said: "I saw the useless suffering, the cruelty, the nastiness, the suffering of children, of families... it's unbearable, it's shameful, the people are dying and (the international community) does nothing."

US journalist Marie Colvin and French photojournalist Remi Ochlik were killed on Wednesday when a rocket hit a makeshift media centre in Baba Amr in the city.

French reporter Edith Bouvier and British photographer Paul Conroy both suffered leg wounds in the same rocket attack.